The long term objective of this project is to study the mechanisms of DNA repair in a model eukaryotic cell, Chlamydomonas reinhardi. The existence of a post-replication repair of ultraviolet light-induced damage in this organism will be examined using alkaline sucrose gradients. This process will also be examined in ultraviolet light sensitive mutants of chlamydomonas. Various forms of DNA polymerase will be characterized from this organism. An attempt to establish one of the forms as a repair enzyme will be made by isolation of a mutant defective in that particular form and correlation with a defective repair system. Isolation and characterization of the various deoxyribonucleases present in this organism will be continued. Evaluation as to their potential role in repair will be carried out based on enzymological properties and correlation with the level of activity in mutants deficient in repair.